Streamline introductory notebooks (#733)

lib/livebook/notebook/explore/distributed_portals_with_elixir.livemd

@@ -195,19 +195,24 @@ Date.from_iso8601("2020-02-30")
 Now, what happens if we want our code to behave differently depending
 if the date is valid or not? We can use `case` to pattern match on
 the different tuples. This is also a good opportunity to use Livebook's
-inputs to pass different values to our code:
+inputs to pass different values to our code. To render inputs, we need to
+install the [Kino](https://github.com/livebook-dev/kino) library:
 
 ```elixir
-# Bring in Livebook inputs
 Mix.install([
   {:kino, "~> 0.3.1", github: "livebook-dev/kino"}
 ])
 ```
 
+Kino allows our code notebooks to control Livebook itself. Let's render
+an input by evaluating the cell below:
+
 ```elixir
 date_input = Kino.Input.text("Date")
 ```
 
+Now we can read its value and parse it:
+
 ```elixir
 # Read the date input, which returns something like "2020-02-30"
 input = Kino.Input.read(date_input)
@@ -222,15 +227,12 @@ case Date.from_iso8601(input) do
 end
 ```
 
-We have been using `IO.inspect` to write values out of the notebook
-and here we used `IO.gets` to read data in. The string passed to
-`IO.gets` must have the same suffix as the input name. The returned
-string is always appended with a newline. Then we remove the trailing new
-line and use `case` to pattern match on the different outcomes of the
-`Date.from_iso8601` function. We say the `case` above has two clauses,
-one matching on `{:ok, date}` and another on `{:error, reason}`.
-Try changing the input and re-executing the cell to see how the outcome
-changes.
+Now try adding a date to the input above, such as `2020-02-30` and
+reevaluate the cell accordingly. In this example, we are using `case`
+to pattern match on the different outcomes of the `Date.from_iso8601`
+function. We say the `case` above has two clauses, one matching on
+`{:ok, date}` and another on `{:error, reason}`. Try changing the input
+and re-executing the cell to see how the outcome changes.
 
 Finally, we can also pattern match on maps. This is used to extract the
 values for the given keys:

lib/livebook/notebook/explore/elixir_and_livebook.livemd

@@ -37,28 +37,6 @@ return the Elixir version.
 Note you can also press <kbd>tab</kbd> to cycle across the completion
 alternatives.
 
-## Imports
-
-You can import Elixir modules to make the imported functions visible
-to all subsequent cells. Usually you want to keep `import`, `alias`, and
-`require` in the first section, as part of the notebook setup.
-
-For instance, you can import `IEx.Helpers` and bring all of the amazing
-conveniences in Elixir's shell to your notebook:
-
-```elixir
-import IEx.Helpers
-```
-
-```elixir
-h(Enum.map())
-```
-
-```elixir
-# Sidenote: http://www.numbat.org.au/thenumbat
-i("I ❤️ Numbats")
-```
-
 ## Using packages
 
 Sometimes you need a dependency or two and notebooks are no exception to this.
@@ -162,50 +140,6 @@ Since this branch is a separate process, a crash has limited scope:
 Process.exit(self(), :kill)
 ```
 
-## Inputs
-
-Livebook supports inputs and you read the input values directly
-from your notebook code, using `IO.gets/1`. Let's see an example
-that expects a date in the format `YYYY-MM-DD` and returns if the
-data is valid or not:
-
-```elixir
-date_input = Kino.Input.text("Date")
-```
-
-<!-- livebook:{"reevaluate_automatically":true} -->
-
-```elixir
-# Read the date input, which returns something like "2020-02-30"
-input = Kino.Input.read(date_input)
-
-# And then match on the return value
-case Date.from_iso8601(input) do
-  {:ok, date} ->
-    "We got a valid date: #{inspect(date)}"
-
-  {:error, reason} ->
-    "Oh no, the date is invalid. Reason: #{inspect(reason)}"
-end
-```
-
-The string passed to `IO.gets/1` must be prefixed with the name you
-assigned to the input. The returned string is always appended with
-a newline. This is built-in on top of Erlang's IO protocol and built
-in a way that your notebooks can be exported to Elixir scripts and
-still work!
-
-You may also have noticed something special about the code cell above.
-After you evaluate it for the first time, it says "Reevaluates automatically"
-instead of showing the "Reevaluate" button. This means the cell will
-automatically reevaluate whenever the input changes or whenever a
-previous cell is reevaluated. Give it a try! You can enable this
-behaviour by clicking the Cell Settings icon (<i class="ri-settings-3-line"></i>)
-after focusing a code cell.
-
-There are many other input types available, give them a try to learn
-more.
-
 ## Evaluation vs compilation
 
 Livebook automatically shows the execution time of each Elixir

lib/livebook/notebook/explore/intro_to_kino.livemd

@@ -5,8 +5,8 @@
 In this notebook we will explore the possibilities that
 [`kino`](https://github.com/elixir-nx/kino) brings
 into your notebooks. Kino can be thought of as Livebook's
-friend that instructs it how to render certain output
-and interact with it.
+friend that instructs it how to render certain widgets
+and interact with them.
 
 ```elixir
 Mix.install([

lib/livebook/notebook/explore/intro_to_vega_lite.livemd

@@ -5,8 +5,8 @@
 To render graphs in Livebook, we need the
 [`vega_lite`](https://github.com/elixir-nx/vega_lite) package
 for defining our graph specification and
-[`kino`](https://github.com/elixir-nx/kino), which augments
-Livebook with client-driven interactive widgets:
+[`kino`](https://github.com/elixir-nx/kino). We won't use Kino
+directly, but it is required to render VegaLite:
 
 ```elixir
 Mix.install([

lib/livebook/notebook/explore/vm_introspection.livemd

@@ -48,18 +48,16 @@ IO.puts node()
 IO.puts Node.get_cookie()
 ```
 
-Now, paste these in the inputs below:
+Now render the inputs below:
 
 ```elixir
 node_input = Kino.Input.text("Node")
-```
-
-```elixir
 cookie_input = Kino.Input.text("Cookie")
 ```
 
-And now execute the code cell below, which will read the inputs,
-configure the cookie, and connect to the other notebook:
+And paste the node name and the cookie value from the other node inside.
+
+Now let's read the inputs, configure the cookie, and connect to the other notebook:
 
 ```elixir
 node =